Conventionally, photocurable resin compositions with high concealability have been widely used for a material for covering a flexible wire board (see, JP 2013-194156 A), a casting material for a duplicate of a prototype model (see, JP 11-060962 A), a black stripe of a lenticular lens (see, JP 2013-082924 A), and adhesives for assembly of an electronic device or the like (see, JP 2014-025021 A) As a representative method for providing a photocurable resin composition with concealability, a method of blending carbon black as a pigment is mentioned. However, since most of active energy ray such as ultraviolet light is absorbed by carbon black while the concealability is obtained, there is a problem that an occurrence of a poor curability is caused if the pigment concentration is excessively high.
With such background, it is described in JP 11-060962 A that, according to a photosensitive resin composition for casting which contains a photo radical polymerization initiator, a leuco dye, a photoacid generating agent, and an ethylenically unsaturated compound, poor curing is not yielded while the cured product has black color, as it utilizes faster generation speed of “radical species that are generated by light irradiation” than “acids that are generated by light irradiation.” Namely, curing is achieved by transmission of light before having the blackening caused by an acid.